Images captured by an image sensor are often stored in compressed form. One such standard compression technique includes the use of a discrete cosine transform (DCT) in accordance with the Joint Photographic Experts Group (JPEG) standard. Images stored using the JPEG compression standard are referred to as JPEG compressed images. Image compression using the JPEG standard is well known.
JPEG compression is a lossy compression scheme, meaning that compression of an image using the JPEG standard results in some data being irretrievably lost. The loss of data is controlled so that, in most cases, the human eye does not perceive the loss that results from an initial JPEG compression. However, each time a JPEG compressed image is decompressed for editing purposes, for example, and then resaved using JPEG compression, the image is recompressed. Recompression results in additional data being irretrievably lost. Multiple JPEG compressions of an image result in noticeable irregularities in the image. Currently, there is much emphasis on developing methods and systems for the lossless editing of JPEG compressed images, thus resulting in image editing that does not require decompression and subsequent recompression.
One type of editing action which is often performed by using JPEG decompression and recompression is the rotation of a JPEG compressed image. A conventional approach to rotating JPEG compressed images requires decompressing the JPEG compressed image into a bitmap, rotating the resulting bitmap, and then recompressing the rotated image into a JPEG compressed image. However, as explained above, the act of recompressing the image results in a noticeable degradation in the quality of the image. This process also requires significant memory storage and memory bandwidth.
Another method for rotating an image is to rotate the image before the image is JPEG compressed. Traditionally, this requires storing the image data as a bitmap and then using a separate buffer memory for remapping the image data. Like the JPEG decompression/compression method explained above, this method also requires significant memory storage and memory bandwidth.
Therefore, there is a desire and a need for methods and systems that facilitate the rotation of image data without requiring full-size memory buffers and JPEG decompression and recompression.